Protocol Online logo
Top : New Forum Archives (2009-): : General Lab Techniques

White residue after 70% ethanol dries? - (Apr/25/2015 )

I've been doing some cell work in a biosafety cabinet and use 70% ethanol to spray down everything that goes into it. I spray my gloves and rub them together and then spray and rub the containers before putting them inside the cabinet. I've been noticing lately that after the ethanol dries that it leaves a white residue on the surface of the containers etc. I've thoroughly washed and rinsed the entire ethanol bottle and filled it up with new ethanol but it still keeps happening. Any ideas?


could be a sign of water impurity?


Or an ethanol impurity. Often the ethanol used to make 70% for the spray bottles is bulk (hence cheap) ethanol, which is full of impurities, some of which are insoluble in water. There might also be some residues from chemicals such as calcium chloride used to dry the ethanol after purification.


Also, many cheap bottles of ethanol have denaturants added to make it toxic for consumption.


We had such a phenomenon when a lab technician prepared 70 % ethanol from 96 % stock with normal tap water instead of demin water, i.e. it's then precipitated calcium carbonate (and other carbonates).


now that I'm thinking about it I remember I've had such problem many times but never realized it was some sort of impurity. we made our 70% from industrial grade, not molecular grade, obviously.


might (partially) be the denaturant - are you using an SD alcohol?

-Phil Geis-